The old 2.x version is quite unstable and causes many, many issues on almost all devices it runs on. That isn't to say that the app is bad, and doesn't work. Because it does work, just not as intended normally. You're much better off shelling out money for a better phone and getting the latest and greatest version. Phones running Android 4.x or greater are usually only about $150 these days, and they, in themselves are far more superior to phones running Android 2.x

Having said that almost all phones running 2.x are at least a couple of years old. It's like upgrading from black and white to colour. So I suggest you get a better phone. WifiKill 2.x was discontinued for a reason